An air belt apparatus is well known which restrains an occupant seated in a seat of a vehicle such as a car to the seat with an inflatable air belt in the event of collision or the like.
Japanese Unexamined Patent Application Publication No. 11-348725 describes, as the air belt, an air belt including a folded member being a bag-shaped belt that inflates with gas introduced therein and is folded in a band shape and mesh webbing covering the folded member of the bag-shaped belt. The mesh webbing is made of a knitted material configured to be flexibly expandable in the circumferential direction of the bag-shaped belt but hardly expand in the longitudinal direction of the bag-shaped belt. During the inflation of the bag-shaped belt, meshes of the mesh webbing spread in the circumferential direction of the bag-shaped belt. As a result, the mesh webbing shrinks in the longitudinal direction of the bag-shaped belt, and the air belt is reduced in length. With the air belt thus reduced in length, the air belt comes into dose contact with the occupant and is capable of tightly restraining the occupant.
Knitting of the knitted material forming the mesh webbing will be described below with reference to FIGS. 6a, 6b, 7a, and 7b. FIGS. 6a, 6b, 7a, and 7b are similar in content to FIGS. 4a, 4b, 5a, and 5b of PTL 1, respectively.
FIG. 6a illustrates a normal knitted material for mesh webbing made of yarn threads 120, in which the plurality of yarn threads 120 are knitted to form a plurality of loops R. The loops R formed by each of the yarn threads 120 are arranged to be alternately shifted in position between the left side and the right side from the upper side toward the lower side of the drawing (hereinafter the vertical direction and the horizontal direction refer to the vertical direction and the horizontal direction in the drawings). The upper end of each of the loops R (the upper end of a loop RB2, for example) winds around the lower end of a loop R of another yarn thread 120 located thereon and adjacent thereto (the lower end of a loop RA1, for example). The lower end of each of the loops R (the lower end of the loop RB2, for example) has the tip end of a loop R of another yarn thread 120 located thereunder and adjacent thereto (the upper end of a loop RA3, for example) winding therearound. Thereby, the loops R are continuously arranged in the vertical direction. Further, in a string of these loops R continuing in the vertical direction, the loops R formed by a pair of yarn threads 120 and 120 adjacent to each other in the horizontal direction (120A and 120B, for example) are alternately arranged (in the order of the loops RA1, RB2, and RA3 from the upper side, for example).
FIG. 6b illustrates the knitted material for mesh webbing with insertion threads 130 inserted in the knitted fabric. The insertion threads 130 are each routed from the upper side toward the lower side along the above-described string of loops R continuing in the vertical direction to alternately pass by the left side and the right side of the loops R. Each of the insertion threads 130 is routed such that, immediately before passing by a side of each of the loops R, the insertion thread 130 passes by a side of a loop R located on and adjacent to the loop R and is drawn from the rear side to the front side of the knitted material, passes the front side of the point of intersection of yarn threads 120 and 120 forming the loop R and the loop R located thereon, and thereafter passes by the side of the loop R and returns from the front side to the rear side of the knitted material. With the insertion threads 130 thus inserted in the knitted fabric, the strength of the knitted material is improved, making it possible to relatively reduce the thickness of the knitted material.
FIG. 7a illustrates a state of the mesh webbing made of the knitted material in FIG. 6b before being expanded. FIG. 7b illustrates a state in which the mesh webbing is expanded in the circumferential direction of the bag-shaped belt in accordance with the inflation of the bag-shaped belt. To form the mesh webbing with the knitted material, the knitted material is arranged such that the strings of loops R continuing in the vertical direction of the drawings extend in the longitudinal direction of the bag-shaped belt. As described above, the mesh webbing (knitted material) hardly expand in the longitudinal direction of the bag-shaped belt. When the bag-shaped belt inflates, the meshes of the mesh webbing spread in the transverse direction, as illustrated in FIG. 7b. As a result, the mesh webbing shrinks in the longitudinal direction of the bag-shaped belt, and the air belt is reduced in length.